The prevalence of overweight children and adolescents has increased significantly during the last two decades. While there are empirically supported weight management interventions for school age children, treatment findings with overweight adolescents are not as consistent. A potential limitation of weight control interventions for adolescents is the minimal attention given to the peer group as an active component of treatment. We have promising findings from a pilot study that involves adding an innovative peer-based intervention (peer-based skills training; PBST) to cognitive behavioral weight management treatment for adolescents. The purpose of the proposed study is to expand the pilot by: 1) increasing our sample size, 2) assessing weight loss over a longer time period, and 3) evaluating the role of psychosocial variables, as well as physical activity and diet, in mediating treatment outcome. It is hypothesized that overweight adolescents randomized to cognitive-behavioral treatment with peer enhancement will demonstrate greater weight loss at long term follow-up than adolescents randomized to cognitive-behavioral treatment with exercise. One hundred and fifty adolescents between the ages of 13 and 16 years and 20% and 80% overweight will be randomized to one of two treatment conditions: 1) Cognitive-Behavioral Weight Loss Treatment with Peer-Based Skills Training (CBT + PBST) or 2) Cognitive-Behavioral Weight Loss Treatment with Exercise (CBT+EXER). Measures of height, weight, physical activity, diet, and psychosocial functioning will be obtained at baseline, end of treatment, 12 months, and 24 months after randomization. A between-groups t-test will be conducted to evaluate group differences in change in percent overweight between baseline and 24 month follow-up . Hierarchical linear modeling will be used to assess the pattern of weight loss for the two treatment groups across four time points: baseline, end of treatment, 12 month, and 24 month follow-up. Effects of treatment of psychosocial measures will be analyzed using mixed analysis of variance with treatment condition as the between subjects factor and a within subject factor of time. Finally, a series of regression analyses will be conducted to evaluate the role of psychosocial variables, physical activity, and diet, as mediators of treatment outcome.